Call processing systems, including voice over Internet protocol (VoIP), may utilize session initiation protocol (SIP). However, fully distributed transfer features typically rely on some non-mandatory SIP messages and/or headers, such as REFER/refer to, INVITE with replace, etc., to complete the transfer.
Unfortunately, these non-mandatory SIP methods/headers may not be supported by third-party devices. Further, if such support by third-party devices is declared, the functionalities may not be as desired by a particular phone system. Accordingly, the transfer feature may not work properly, or at all, resulting in interoperation and/or integration problems.